Black Hair/Brunettes are mon common in general, so when i can find a blond that match the look and services i want, it will usually be what will draw me to her. For exemple a blond with big breast doing cim/cof in the vein of pornstars of the USA like Jenna Jameson in her prime is the fantasy i was looking for. Now does not mean i won't be attracked to darker hair girls for any reasons. Sometimes her charm and persona could be a factor or something special in her look.
Lets just say in general i prefer girls with shoulder and + lenght hair (nor a fan of very short haircuts) and blond is my favorite, jet black is second and fire red would be third. I also like bright blue but that is very uncomon and sadly when a girl color her hair blue, she is often in the "punk" style so either she has too many piercing, weird haircuts or is plainly not my type for the rest.
As for half shaved or both side shaved, i HATE this trend, but i can pass over it if the girl please me for the rest, but i wish she wouldn't had do that for sure. I saw girls with long beautifull hair get an half shaved and to me it was like painting a mustache on the mona lisa...
ANYWAY... basically it will always be a combo of things when i like a look or not, but most of the time i prefer girls blond... beside a few rare exeptions where black suit her better, most of my favorite pornstars i always tough where hotter as blonds (madison ivy, diamond foxxx, monique alexander to name a few)
In term of escorts, i didn't much girls that changed there hairs for a second booking or such, the only one is Kaila, saw her as jet black last year, and blond this year, i think even tough she is pretty with black hair, she get way hotter as a blond. But thats personaly opinion of course.